This application claims the priority of German application 197 17 069.2, filed Apr. 23, 1997, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to an independent wheel suspension for steered wheels of motor vehicles, particularly passenger cars, in the form of a three-arm anti-squat suspension.
Three-arm anti-squat suspensions typically comprise a lower A-arm, a wheel carrier connected therewith and guided on its upper end by way of a camber strut, and a connecting rod which connects the wheel carrier, offset to its linking to the A-arm, additionally with the A-arm and thereby supports it transversely to the plane defined by the linking points of the wheel carrier on the A-arm and of the camber strut on the wheel carrier and on the vehicle body. For aligning the wheel, the wheel carrier is additionally provided with a steering knuckle arm to which the tie rod is linked, whereby the wheel can be actively steered by way of the tie rod in connection with a steering gear.
With respect to steering movements, a swivelling of the wheel about a virtual axis is carried out in the such known three-arm anti-squat suspensions. The virtual axis is represented as an intersection line of two planes; specifically, the first of the two planes is defined by the linking points of the camber arm and the linking point of the wheel carrier on the A-arm, and the second of the planes is defined by the linking points of the connecting rod on the wheel carrier and the A-arm, and the linking point of the wheel carrier on the A-arm.
During steering movements which, in fact, take place by swivelling the wheel carrier and displacing its linking points, as the result of the corresponding displacements, the wheel is therefore placed in a position which would occur during the swivelling about the virtual axis. Because the virtual axis is set by the above-mentioned planes, specifically the first and the second plane and is not defined by the real linking points, the phase-shifted dynamic forces of the individual arms which act in these planes also result in torques about the real axis. Such dynamic forces are critical with respect to the steadiness of the steering of the vehicle. Correspondingly, wheel suspensions of this type, as known, for example, in JP 4-372 408 (A), are also sensitive with respect to elasticities in the many linking points which exist in such a wheel suspension.
Furthermore, in known wheel suspensions, in the frontal view, with an S-shaped curvature, the wheel carrier is relatively strongly curved toward the inside. Thus, in conjunction with a connecting rod which is upright in the frontal view but is clearly sloped toward the front in the lateral view, and with linking points of the wheel carrier on the A-arm and on the camber arm which, in the frontal view, are situated almost vertically above one another, while the real steering axis defined by these linking points is sloped toward the rear and upward, a relatively large space requirement exists for the wheel suspension and, during steering movements, relatively large spatial displacements will also occur for individual wheel suspension elements, which, in addition to effects partially endeavored for the wheel suspension, also has effects on the installation volume.
JP 07 047 824 A describes another three-arm anti-squat suspension, specifically for non-steered wheels of passenger cars, in which the wheel carrier is guided by way of a lower A-arm and an upper camber arm and is additionally supported by a connecting rod with respect to the A-arm. Furthermore, a steering knuckle arm is mounted on the wheel carrier and is supported elastically against the vehicle body by a tie rod extending in the transverse direction. The connecting rod, starting from the forward interior end area of the A-arm, extends diagonally toward the rear upwards against the wheel carrier. The second plane set by the linking points between the A-arm, the wheel carrier and the connecting rod and the first plane defined by the linking points of the camber arm and the linking point of the wheel carrier on the A-arm cross one another and have an intersection line which, starting from the linking point of the wheel carrier on the A-arm, both planes have in common. The intersection line also extends in the area of the linking point of the wheel carrier on the camber arm so that the virtual and the real steering axis have a similar course and, also in the area of the linking point of the camber arm on the wheel carrier, do not have a very large displacement. However, this displacement is desirable because this three-arm anti-squat suspension intended for non-steered wheels, in conjunction with the elastic support of the tie rod with respect to the vehicle body by swivelling the wheel carrier under the influence of longitudinal and lateral forces, must result in steering effects, specifically, under the influence of lateral forces, in the toe-in direction and, under the influence of longitudinal forces, in the toe-out direction, which result in a stabilizing of the vehicle.
An object of the present invention is to provide an improved wheel suspension to overcome the disadvantages and susceptibilities found in conventional suspensions.
According to the present invention, this object has been achieved by providing that the first plane defined by the linking point of the wheel carrier on the A-arm and the linking points of the camber arm and the second plane defined by the linking point of the wheel carrier on the A-arm and the linking points of the connecting rod have an intersection line which, starting from the linking point of the wheel carrier on the A-arm which the two planes have in common, in the upper area of the wheel carrier extends at least almost through the linking point of the wheel carrier on the camber arm. In top view, when the connecting rod is upright, the straight connection line between the linking points of the connecting rod on the wheel carrier and of the wheel carrier on the camber arm extends at an angle of approximately 45.degree. with respect to the longitudinal plane of the vehicle which opens toward the outside in the driving direction.
Consequently, the virtual steering axis will practically coincide with the axis of rotation of the wheel carrier so that forces acting in the above-mentioned planes, particularly also dynamically acting forces (thus forces acting by way of the camber arm and the connecting rod) are always aimed at the steering axis and therefore result in no torques about the steering axis and therefore also neither generate a wheel fight nor impair the straight-ahead driving.
In addition to a wheel suspension construction which is compact in the longitudinal direction of the vehicle, the present invention also achieves, in connection with large steering angles, that the individual wheel suspension members experience only slight displacements so that, irrespective of possible large steering angles, a very compact construction can be implemented. Nevertheless, with increasing steering angles, a certain displacement of the steering axis is achieved, in the sense of an enlargement of the caster offset, in the upper area toward the rear which results in an increased aligning torque in the event of steering angles.